Update 2010/07/10: There have been some concerns expressed over recent seismic activity at Volcano Katla. There is nothing being reported from the Icelandic Met Office that indicates a concern. Active volcanos tend to have regular periods of seismicity. These recent events are of low magnitude and are not believed to be indicative of imminent eruption of Katla. The earthquake charts on the Met site are updated constantly (near real-time according to the Met Office) and the colours do not indicate severity, only time elapsed since last occurred. Earthquakes greater than magnitude 3 are indicated by a star icon.
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Update 2010/04/24: Note: This will be EWR’s last report on the current event sequence at Eyjafjallajökull unless there is a substantial change in events. I invite you to explore the links included throughout this post to develop an understanding of the Eyjafjallajökull event. The Active Monitoring sidebar will continue to list the quicklinks for NORDVULK and the webcams. This post will be added to the general Active Monitoring list for quick access as the EWR blog moves forward.

The bulk of the information presented has been drawn from situation reports of the Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland. Certain links contained below represent specific research efforts of indviduals and are attributed where appropriate. As has been noted in this latest sitrep, the eruption has not ceased and there remains concern about future activity. While Katla is not considered at immediate risk of eruption, the association with Eyjafjallajökull means it will continue to be monitored.

Tephra fallout: Minor (plume dark but no reports of fallout in districts around volcano)
Meltwater: 100-120 m3/s, based on gauge at old Markarfljót bridge and a rough estimate of base flow.

Conditions at eruption site: North crater still active. Mild explosive activity with spatter thrown to 100 m height above crater. Shockwaves occur every few seconds. North of crater a roughly 300 m long and wide depression has been melted out in the last three days. Steam plumes rise from the depression, especially at the margins. This is explained by lava flowing northwards from the crater with the steam rising where lava meets ice.

Seismic tremor: Magnitude similar to what it has been over the last few days.

Overall assessment: Magma flow rate has remained at similar level over the last few days. Plume activity is gradually declining. Flow of lava is considered to have began around noon on Wednesday 21 April. Timing is based on: a) onset of semi-continuous discharge of meltwater from Gígjökull, b) Observations of steam rising at northern margin of ice cauldon at 1300 on 21 April, and c) a change occurs in fluctuations in tremor amplitude at this time. No signs of melting or meltwater discharge towards south. No signs of termination of eruption.

Eruption update 21 April

Eruption continues with less explosive activity. Eruption rate is inferred to have declined over last few days and now be an order of magnitude smaller than during the initial 72 hours of the eruption. Present eruption rate is estimated to less than 30 m3/s of magma, or 75 tonnes/s , with a large uncertainty.

Eruptive style: The northernmost one of two main craters in the summit caldera is active. Phreatomatic explosive activity occurs with some lava spatter at craters.

Plume height: about 3 km

Tephra dispersal: local towards the south

Meltwater: minor, but what is melted flows down into Markarfljót, no signs of water accumulation in craters

Seismic tremor recorded by the Icelandic Meteorological Office: some fluctuations but mostly stable. Tremor is not decreasing and does not reflect the decline as inferred for the eruption rate.

GPS-measurements: indicate continuing small pressure decrease under the volcano at a similar rate.

Composition of erupted material: Samples collected April 19 show same composition as early in the explosive phase, but fluorine content is higher. Samples collected 19 April have 850 mg/kg (initially it was 25-35 mg/kg). This is due to the change in eruptive style – tephra is now not washed to the same extent by water in the eruptive plume.

Amount of erupted material: Uncertain but on the order of 100 millon cubic meters. Tephra next to craters is 20-30 m thick.

Radar images acquired yesterday, 20 April, by the Icelandic Coast Guard showed no changes in the size of the cauldron at the eruption site of Eyjafjallajökull, compared with images from 19 April – Eyjólfur Magnússon

20. April 2010: Latest results from GPS stations around Eyjafjallajökull show deflation associated with the eruption. No movements associated with the Katla volcano are presently observed – Benedikt Ófeigsson, Sigrún Hreinsdóttir and Bryndís Brandsdóttir

Explosive activity at the eruptive site and seismic tremor continue at a relatively stable rate without a decline overnight. Air space over large part of Europe continues to be closed. Eruption plume loaded with tephra (ash) rises to more than 8 km, with tephra fallout in inhabited areas around the volcano. Over 20 lightning recorded in the eruption plume over a 4 hour period. Overnight wind conditions at the eruptive site change. Steady easterly wind that have prevailed since the onset of the explosive eruptive phase replaced by northerly winds that carry the eruption plume away from the volcano to the south. A MODIS satellite image at 03:41 GMT shows the eruption plume bending from south to east, and a NOAA AVHRR satellite image acquired at 07:01 GMT shows plume heading from the volcano towards the south.

Impact on European Air Travel 2010/04/17 13:25 UTC. Normally the airspace over the United Kingdom, Scandanavia and northern Europe is full of planes.

GPS measurements from Thorvaldseyri (THEY), south of the Eyjafjallajökull volcano, now show displacement towards north. The station had been moving south since the intrusion activity started in the end of December. This change suggests that an equillibrium has been reached in magma flow in and out of the volcano.Plot showing the displacement (pdf file – data from Sigrún Hreinsdóttir, runa@hi.is)

Eyjafjallajökull eruption: A new phase started on 14 April 2010
A new phase of the Eyjafjallajökull eruption started around midnight on the 14th of April, where melt penetrated its way to the central crater beneath the glacier. Bad weather makes visual observations difficult, but surveillance flights with radar and temperature sensors will shed light on the new conditions later today.

20 March, late evening: An eruption begins on Fimmvörðuháls located between the Eyjafjallajökull and Mýrdalsjökull ice caps. The eruption was initially detected visually; a red cloud above eruptive site was seen around 23 GMT. The onset of the eruption was gentle, following a period of weeks and months prior to the eruption of high seismic activity and high crustal deformation rates in the Eyjafjallajökull volcanic system. Seismic tremor begins around 22:30 and rises gently. Seismicity was not enhanced significantly immediately prior to the eruption compared to the weeks prior to the eruption. However, the depth of earthquakes decreases and earthquake propagate from magma upwelling area under Eyjafjallajökull towards the eruptive site.
21 March: Observations from air in early morning reveal a short (<500 m) NE-SW oriented effusive eruptive fissure with fire fountaining and Hawaiian eruptive style. Fire fountains occur from 10-12 vents, with lava jets reaching up to about 100 m hight. The eruption appeared stable from 4-7 AM when viewed from air. The eruption tremor rose gently until reaching a maximum around 7-8 AM. No further lengthening of the fissure was detected. Lava is limited to immediate surroundings of the eruptive craters (less than few hundred meters). Minor amount of ash falls within few km to the west of the eruption site, carried by easterly winds. No ice melting is occurring as the eruptive fissure is just outside the ice covers of Eyjafjallajökull and Mýrdalsjökull.
22 March: Initial observations from ground. Activity had focused on a series of closely spaced vents. Prevailing easterly winds lead to maximum scoria accumulation on a linear rim west of the NE-SW oriented fissure. Lava flows (Aa type) towards the Hrunagil canyon with initial view on a spectacular „lava fall“ as molten lava flows off steep cliffs into the canyon.
23 – 31 March: Steady eruptive activity in initial craters with gradual focusing towards fewer vents. Lava flows towards north into two canyons, Hrunagil and Hvannárgil, with intermittent spectacular „lava falls“ as molten lava flows off steep cliffs into both canyons. Extensive steam plume generation when magma melts snow in front of advancing lava, mostly in the canyons. Two or three plumes observed (one at the eruptive craters, others more pronounced in front of the advancing lava). Meltwater released in batches into rivers in the canyons. Relatively steady eruption tremor recorded by seismometers.
Evening of March 31: Opening of a new short fissure immediately north of the previous one probably relating to changes at shallow depth in the feeder channel (few hundred meters?). No change in eruption tremor.

31 March – April 6: Activity continues in both the old and new eruptive craters, in a similar manner as before, with lava mostly flowing towards the NE, and pronounced „lava falls“ in Hvannárgil. Last active phase of the of the lava fall into Hrunagil on 31 March.

April 5: Eruption tremor (1-2 Hz frequency band at nearest seismic station Godabunga) begins to decline in a gradual manner.

April 7: Activity has stopped in the original craters of the eruption, and is limited to craters on the new fissure formed on 31 March. Lava flows cover an estimated area of 1.3 square kilometers, with estimated average thickness of 10-20 m. Maximum elevation of scoria craters formed in the eruption is 82 m.
April 9: After little change in deformation rates during the eruption, timeseries at continuous GPS-stations north of the volcano show sudden change, partly jumping back to pre-eruptive levels. Signals may relate to decreasing pressure in the magma conduit feeding the eruption.
April 11: Eruption tremor approaches pre-eruptive levels, but visual observation reveal eruptive activity in late afternoon.

April 13: Extensive seismic swarm begins around 23:00 under the central part of Eyjafjallajokull.

April 14: Onset of seismic tremor shortly after midnight of increasing amplitude, in association with an eruption from a new vent under the central ice-capped crater of Eyjafjallajokull. The eruption is visually confirmed in early morning – eruption plume rises above Eyjafjallajokull. Meltwater forms a jokulhlaup.

A view from space on the crustal deformation associated with magma intrusion – preceding the March 20th eruption
First interferometric analysis of synthetic aperture radar images acquired by satellites reveal extensive deformation associated with a magmatic intrusion under Eyjafjallajökull preceding the eruption. The deformation signal appear as colour fringes, where each fringe represents a change in range from ground to satellite of 1.5 cm. Extensive deformation is observed both north and south of Eyjafjallajökull. The two images show a large change in range from ground to satellite between September 1999 and March 20, 2010, just prior to the eruption that began around 22:30 GMT. These are the first in a series of interferograms anticipated to be formed showing the course of the eruption.
The interferograms are formed by analysing images from the German TerraSAR-X satellite. The research is a collaborative project between the Nordic Volcanological Center at the Institute of Earth Sciences, University of Iceland, the Technical University of Delft, Netherlands, and the University of Wisconsin-Madison, USA. The initial interferograms have been formed by Andy Hooper at Delft.
Contact persons: Rikke Pedersen (rikke@hi.is), Martin Hensch (martinh@hi.is), Andy Hooper (a.j.hooper@tudelft.nl), Kurt Feigl (feigl@wisc.edu), Amandine Auriac (ama3@hi.is), Freysteinn Sigmundsson (fs@hi.is)

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Saturday night, Mar 21, 2010, at about 11:30, residents of Fljotshlid, Iceland, noticed an orange flare from the vicinity of the Eyjafjallajökull glacier.

A kilometer long fissure has opened in a passage in Fimmvörduhals, between glaciers Eyjafjallajökull and Mýrdalsjökuland and volcanic magma was erupting up through the fissure.

Scientists say the eruption seems to be small and since it is not under a glacier, the danger is less than it might have been.

An Icelandic Coast Guard aircraft flew over the eruption early this morning. For three hours the plane circled the area and Karl Sigurbjörnsson of RÚV filmed this dramatic video of the eruption (do watch the video – the images are quite spectacular).

The immediate area was evacuated and has been closed to travel. This is a popular tourist area of Iceland, and there is a well-known hiking trail in the vicinity of the eruption. Residents have been allowed to return, but the area remains closed to tourists.

There are concerns that the eruption could spread to beneath the glacier, and there also a watch on Katla (see also Katla Volcano at the Institute of earth Sciences ), a nearby large, presently dormant, volcano. Katla has erupted before, and eruptions under glaciers are especially serious due to rapid melting of large volumes of ice, creating near instant high volume floods.

There have been small earthquakes and seismic activity in the area. Seismic activity in Eyjafjallajökull has been intensive for the past three weeks and most of the earthquakes have been located between 7 and 10 km depth. On March 19th a seismic swarm began east of the top crater, originating between 4 and 7 km depth. The activity migrated eastwards and towards the surface on Saturday, March 20th. At 22:30 GMT a slightly increased tremor was detected on three seismic stations, located within 20 km from the volano’s top crater, and within the next two hours reports on an volcanic eruption were received. (from Icelandic Met Office)

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